Reasonably-pure drinking water is an absolute necessity of life and clean, fresh-tasting drinking water is one of its pleasures. Most persons in well-developed countries like the United States have access to safe, reasonably-pure drinking water. But even in areas having water suitable for human consumption, such water may contain minerals, e.g., iron and calcium, and/or chemicals and other substances.
While such non-water constituents may not be harmful to humans, they often impart an unpleasant taste or odor to the water. And normally-high-quality drinking water sometimes contains bacteria or other microorganisms which may impart a bad taste to the water or otherwise impair its quality. Often, such an eventuality results from a temporary deficiency in the water treatment facility.
One well-known approach for removing impurities from drinking water is distillation. Distillation involves boiling water to form water vapor and then cooling such vapor to a temperature below the condensation temperature, i.e., below about 212.degree. F. The resulting liquid, sometimes referred to as condensate or distillate, is collected for drinking or the like. Distillation separates pure water from the entrained minerals and other potentially bad-tasting impurities. And quite aside from improving the sensory quality of water, the high temperatures involved in the process are sufficient to kill many types of potentially-harmful microorganisms.
Water distillers commonly use a heating coil to boil, as steam, the water from a raw water container. A fan blows air across condensing coils which cools the steam and condenses it back to now-purified water. The distiller electrical circuit usually has some type of automatic shutoff apparatus involving a thermostat to shut down the distiller when the water in the raw water container is nearly exhausted.
A reason for doing so (rather than let the distiller "boil dry") is that retention of residual water helps reduce the amount of scale and deposits which form in the raw water container. And shutting off the apparatus while some residual water remains may also prolong the life of the water heating element.
The distiller disclosed in U.S. Pat. No. 4,269,663 (McFee), a type of batch distiller, has a thermostat and auxiliary heater on its exterior. At a sufficiently-low water level, the temperature of the auxiliary heater rises and such rise is sensed by the thermostat which opens to disable the main heater.
U.S. Pat. No. 4,662,102 (Diebel) discloses a distillation apparatus having a spring-biased support platform. When the water level diminishes sufficiently, a spring biased the platform upwardly to a position which shuts off the thermostat. The distiller discloses in U.S. Pat. No. 5,059,287 (Harkey, Sr.) controls heating element shutoff by sensing air temperature above the heating element which is exposed because of water depletion. A seeming difficultly with the Harkey, Sr. distiller is that because the thermostat is not in surface contact with a good heat-transfer medium, i.e., metal, reaction time may be slow.
U.S. Pat. No. 5,492,602 (Vogelman et al.) discloses a water purifier with a three-step tray having a heater element at the tray bottom. A side-mounted temperature sensor senses when water above the two upper steps has been evaporated and opens an infeed valve to flow more water into the tray. The Vogelman et al. purifier may be characterized as a continuous, rather than a batch, purifier.
While these prior art arrangements have been generally satisfactory for the intended purpose, they are not without disadvantages. For example, the McFee distiller requires both main and auxiliary heaters. Plural heaters adds to cost and circuit complexity. And, seemingly, the auxiliary heater is exposed for inadvertent touching by the user.
The apparatus of the Diebel patent has a number of electrical components including two arm-operated microswitches and a float-operated microswitch. The electrical circuitry connecting such microswitches and other components seems relatively complex and difficult to manufacture.
The purifier of the Vogelman et al. patent also seems relatively complex in that it uses a microprocessor-based controller coupled to a switch, demister electrodes, a temperature indicator and an on-off function. The microprocessor controls a valve, a fan and other functions.
A distiller having an improved automatic shutoff feature which addresses shortcomings of the prior art would be an important technical advance.